The term “hybrid electric vehicle” is usually used in the art to indicate a four-wheeled vehicle with a drive system including an internal-combustion engine and at least one electric traction motor. The term “electric traction motor” is used to distinguish an electric motor utilized for vehicle propulsion from all other electric motors that may be employed in a vehicle. Hereinafter, the shorter term “traction motor” is also frequently used to indicate an electric traction motor.
The sources of electric energy for the electric traction motor(s) are usually an electric generator driven by the internal-combustion engine, and an electric traction battery charged by the electric generator. In some hybrid electric vehicles, the electric traction battery is also arranged to be charged by an external source of electric energy when the vehicle is parked. The term “electric traction battery” is used to distinguish the large high-voltage electric battery used for powering the electric traction motor(s) from the standard low-voltage electric battery, which powers the other electric system of the vehicle. Hereinafter, for abbreviation, the shorter terms “electric battery” and “generator” are frequently used instead of the terms “electric traction battery” and “electric generator” respectively.